In a known doser-dispenser, for example disclosed in German Patent DE-3 024 489, the intake flap is disposed in the dosing chamber and serves as check valve opening and closing automatically solely as a function of the ascending and of the descending movement. In addition, the intake flap is guided directly on the piston and the return spring of said valve is provided at the level of the central passage of the piston. This results in a considerable lack of precision in the dosage, particularly when the product to be dosed is of pasty consistency. In addition, the known doser-dispenser does not lend itself to maintaining sterility inside the supply and dosing chambers.